Adding fileStream information to documentation

找到描述 stringifier 和传输流的文档，然后将其与 issue 中的文件流示例进行比较。更新文档，使读者了解如何将数据通过管道传输到 fs.createWriteStream，以及是否需要调用 fileStream.end()；当文件流工作流程和流关闭行为都清晰时即完成。

It might be helpful to include some documentation for people who are unfamiliar with transfer streams (like I was until I asked chatGPT). The docs mention that the stringifier writes to a transfer stream, but this is a subtle, and many people are likely to miss that detail or read through it because they don't know what it means.

Here is the code I wrote that can handle file streams:

import jsonlines from "jsonlines"
import fs from "fs"
import path from 'path'

export default function example () {

  // I created a folder in my repo caled "files", and the stringifier will write to it (only locally, don't try this on something like Heroku)
  const outputFilePath = path.join('files', 'jsonl-testing.jsonl')
  const fileStream = fs.createWriteStream(outputFilePath)

  const stringifier = jsonlines.stringify()
  stringifier.pipe(fileStream)
  stringifier.write({
    "prompt": "Question: What is the meaning of life?\n\n###\n\n",
    "completion": "Answer: 42.\n\nEND"
  })
  stringifier.write({
    "prompt": "Question: What is not the meaning of life?\n\n###\n\n",
    "completion": "Answer: not 42.\n\nEND"
  })
  stringifier.end()
  fileStream.end() // do we need to do this? Docs do not specifiy
}